Due to the rapid development of internet and mobile communication technologies, the need for transmitting big data is getting higher and higher. The transmission speed by way of electronic signals seems to have reached a bottle neck. Therefore, the requirement on new transmission means is increasing. For example, the use of optical signals in data transmission paths as an artery would become a trend in the near future. Please refer to FIG. 1, in which a conventional optical transceiver is schematically shown. In the optical transceiver 1, an equalization module 11 functions for diminishing attenuation and jitters of an electronic signal. The electronic signal is then converted into optical signals carrying a large amount of data by an optical transmitter 12, which includes a laser driver 120, a laser light source 121, a monitor photodiode (MPD) 122, and an automatic gain controller (AGC) 123. The optical signal is transmitted to an optical receiver 14 via an optical fiber 13. The optical receiver 14 mainly include an optical detector 141, a trans-impedance amplifier (TIA) 142, a clock and data recovery (CDR) circuit 143 and a pre-emphasis circuit 144 for converting the received optical signal into a corresponding electronic signal, and then outputting the corresponding electronic signal.
Please refer to FIG. 2, in which the structure of an active optical cable (AOC) formed on the basis of a silicon optical bench (SiOB) is schematically shown. An integrated circuit (IC) chip 120 is formed with the equalization module 11 and other associated circuitry, e.g. the laser driver 120, the monitor photodiode 122 and the automatic gain controller 123, and functions for outputting the electronic signals carrying the data to a laser light generator 22 via an external metal wire 201 and a transmission line 211 of a silicon optical bench 21, thereby generating the optical signal. The laser light generator 22 may be implemented with the laser light source 121 as shown in FIG. 1, e.g a vertical cavity surface emitting laser (VCSEL). The laser light signal generated by the laser light generator 22 implemented with the vertical cavity surface emitting laser is injected onto a 45-degree reflective surface 210 of the silicon optical bench 21, reflected to an optical fiber 23, and then transmitted to another silicon optical bench 25. By way of a 45-degree reflective surface 250 of the silicon optical bench 25, the optical signal is inputted into the optical detector 141. In general, the trans-impedance amplifier 142, the clock and data recovery circuit 143 and the pre-emphasis circuit 144 are formed on an integrated circuit (IC) chip 26. Through an external metal line 261 and a transmission line 251 of the silicon optical bench 25, the IC chip 26 is electrically connected to the transmission line 251 of the SiOB 25.
When the transmission speed is required to be higher and higher in order to meet commercial needs, for example expected to increase from 10 Gbps to 40˜100 Gbps, the vertical cavity surface emitting laser technique would not be a good choice any more due to high cost of elements such as the laser light source 121 and the laser driver 120, and technical problems. Instead, a complementary metal-oxide-semiconductor (CMOS) photonics platform is used. The CMOS photonics platform allows most of the elements included in the optical transceiver 1 as shown in FIG. 1 to be formed on the same silicon substrate by way of a CMOS manufacturing process. In this technique, the laser driver 120 and the laser light source 121 are replaced with a Mach-Zehnder interferometer (MZI) as shown in FIG. 3.
It can be seen from FIG. 3 that in a typical Mach-Zehnder interferometer, an input waveguide 30 is divided into an upper waveguide 31 and a lower waveguide 32. With no voltage applied, light is coupled to form an output waveguide 33, and meanwhile, an “ON” signal is generated. Once a proper voltage is applied to a phase retarder 35, the voltage changes the refraction index of the waveguide so that in the path of the upper waveguide 31, light is retarded with half a wavelength, or 180-degree phase. Accordingly, the energy of light in the two optical paths become offset so as to generate an “OFF” signal. Therefore, by controlling the operation of the phase retarder 35, the laser light source which continuously emits laser light can exhibit “ON” and “OFF” effects without directly control the power of the laser light source. Consequently, circuitry complexity can be largely reduced and transmission speed can be significantly enhanced.
As shown in FIG. 4, a cross-sectional view of a CMOS photonics platform is schematically shown. A waveguide structure 40, a grating structure 41, a transistor structure 42 and a modulator structure 43 are formed on a silicon substrate 4. The waveguide structure 40 includes a variety of elements, e.g. a light input nanotaper, light splitter, light filter, light coupler, and light output nanotaper, functioning for receiving the external laser light and transmitting the modulated optical signal to the external optical fiber (not shown). The grating structure 41 mainly functions as a Bragg grating. The transistor structure 42 functions as a phase shifter and a waveguide detector. The modulator structure 43 functions as the MZI modulator as shown in FIG. 3.
Please refer to FIG. 5, in which the packaging of a CMOS photonics platform 51 and an edge emitting laser source 52 via an interposer 50 according to prior art is schematically illustrated. The edge emitting laser source 52 is disposed on a submount 53, and configured in a manner that the light outlet of the edge emitting laser source 52 disposed outside is at a level consistent to the level of the light output end of the optical waveguide structure (not shown in this figure) of the CMOS photonics platform 51. Since the optical signal 520 emitted from the edge emitting laser source 52 is diffracted by a slit, and then passes a collimator, an isolator and a condenser lens (not shown) to couple to the optical waveguide structure of the CMOS photonics platform 51, the condenser lens is adjusted by way of active alignment. When aligning and assembling operations are performed, the edge emitting laser source 52 has to keep operating to generate the optical signal 520. Meanwhile, the coupling effect needs to be detected in real time by way of image processing. Then feedback control is performed to locate optimal assembling position, where the light coupling effect of the optical signal to the waveguide structure 40 as shown in FIG. 4 is optimized. Acceptable deviation in the active alignment process is about +/−4 μm in each of the three axes. Shift deviation beyond the acceptable range would make the optical signal unable to couple to the waveguide structure 40 with a satisfactory light coupling efficiency. In the prior art, it is relatively easy to control the shift deviation in the X-axis and the Y-axis, but the shift deviation in the Z-axis, i.e. in the height dimension, is hard to be controlled. Therefore, the optoelectronic device needs current transmitting therethrough for operations. In addition, the assembling equipment needs additional power supply and detecting circuit, which renders high cost and complicated assembling. The relatively long assembling time is disadvantageous to batch production. Furthermore, assembling deviation might be even worse due to imprecise thickness of the solder layer 501 between the interposer 50 and the CMOS photonics platform 51, as well as imprecise thickness of the interposer 50 and the CMOS photonics platform 51 themselves. Moreover, the thickness of the edge emitting laser source 52 and the submount might also be imprecise, and thus the overall deviation might exceed +/−4 μm.